Add generic feature to set any valid Undertow option

[bdw429s]

Runwar has support for many of the undertow options, but it would also be handy to have a generic approach for any edge case options or new options that a user needs to tap into that we don't have first-class support for yet.

http://undertow.io/undertow-docs/undertow-docs-2.0.0/index.html#options

[denuno]

I'm thinking a xnioOptions="SOME_OPTION=2345,ANOTHER=woohoo" as the format, think that would work for everything?

On a semi-related note, I like JSON files to represent the data, so where we're storing lists (welcome files, and potentially this), I'd prefer to convert them to arrays, and store that in the JSON instead, just so we can eventually have a schema and verify things easier (and stuff like array.add(thing) over splitting/handling [trailing] commas, etc.). Just something to keep in mind, maybe for v5.

[bdw429s]

That format works ok so long as we won't have an equals sign or command in a setting name or value. Or, at least, have a way to escape them.

[bdw429s]

I've had the need for this come up several times recently. Ususally in regards to invalid URL chars that web servers like IIS let through but Undertow chokes on unless you set a special option.